Semiconductor laser devices, such as double heterostructure laser diodes, are utilized in various applications, such as for optical sources in fiber optic communications. In the manufacture of such devices, double heterostructures are grown and processed on a wafer substrate by, for example, liquid phase epitaxy. The wafer is then cleaved into typically solid rectangular laser bars containing many laser diodes. The laser diodes are functional at the laser bar level, and therefore electrical testing is often performed at this level prior to dicing the individual laser diodes from the bars.
Each laser bar has two end faces, or facets, formed by cleaving during the cleaving process. Laser light is ultimately transmitted through the facets, so it is important for their surfaces to remain unperturbed and uncontaminated during handling of the laser bar. Following the cleaving operation on the wafer to form the laser bars, the facets are coated with an optical coating in a facet coating apparatus. A facet coat holding fixture is typically employed to retain the laser bar during the facet coating and also to transport the bar into and out of the facet coating apparatus.
FIGS. 1 and 2 illustrate a conventional facet coat holding fixture 10 for retaining a laser bar 20 during a facet coating operation. The fixture 10 includes a plurality of fixture blades 12. Each fixture blade 12 includes opposing sides 14, 16. A laser bar 20 is placed between a side 14 of one fixture blade 12 and a side 16 of another fixture blade 12. A compression device (not shown) provides a compressive force in the direction shown onto the fixture blades 12 such that the laser bars 20 are sandwiched therebetween.
Each laser bar 20 is a thin, solid rectangular bar having facets 26, 28 on opposing sides. Each laser bar 20 is of a small size. For example, typical dimensions of a laser bar 20 are on the order of 0.005 inches by 0.012 inches by 0.300 inches. Because of its small size, each laser bar 20 must be handled with care to avoid damaging it.
During the compression of the fixture blades 12, the flat side surfaces 14, 16 of two fixture blades 12 compress against two opposing non-facet sides of each laser bar 20. Once the compressive force is applied, the facets 26, 28 of the laser bars 20 can be coated.
After being transported outside of the facet coating apparatus, the compressive force is released from the fixture 10, thereby allowing separation of the laser bars 20 from the fixture blades 12. FIG. 2 shows an exaggerated separation of the fixture blades 12 for clarity of illustration.
Once a laser bar 20 becomes completely separated from a fixture blade 12, the laser bar 20 may be removed by way of a vacuum pick, robot arm, or other similar device for subsequent processing and testing operations.
One drawback to the facet coating operation is that optical coating applied to the facet surfaces 26, 28 of the laser bars 20 often seeps in between the non-facet surfaces of the laser bar 20 and the side surfaces 14, 16 of the fixture blades 12. The result of this seepage is that often, upon release of the compressive force from the fixture 10, a laser bar 20 will stick to one of the fixture blades 12, as shown for the middle laser bar 20 in FIG. 2.
If a laser bar 20 remains adhered to a fixture blade 12, an additional operation is then required to detach the laser bar 20 from the fixture blade 12. One example of such an additional operation includes manually shaking the fixture 10 to loosen the laser bar 20. Another example is physically prying the laser bar 20 from the fixture blade 12 with a pick or other similar device. Such operations result in a reduction in the yield of usable laser bars, since a number of the laser bars 20 become damaged when pried or shaken from the fixture blades 12. Typically, as many as half of the laser bars 20 may become damaged from these additional operations.